Biometric authentication technology is technology that performs personal identification by using biometric characteristics such as fingerprints, palm prints, palm shapes, veins, faces, etc. When personal identification is conducted, biometric characteristic obtained from a living body that is an authentication target is compared (checked) with biometric characteristics that are registered in advance, and authentication for the living body that is the authentication target is conducted on the basis of the similarity between them.
Vein authentication for example is a biometric authentication technique based on biometric characteristics obtained by capturing images of vein patterns under the skin. Because vein patterns are bodies' internal information, vein authentication has a feature of higher safety than biometric authentication based on finger prints, palm prints, palm shapes, faces, etc., which are information on bodies' surfaces. When vein authentication is conducted, illumination light is cast onto a living body and an image of a vein pattern is captured.
Biometric authentication techniques using visible light and near-infrared light as illumination light are also known (see Patent Documents 1 and 2 for example). Techniques of removing the influence of external light from captured images are also known (see Patent Documents 3 and 4 for example).    Patent Document 1: International Publication Pamphlet No. WO 2013/146761    Patent Document 2: Japanese Laid-open Patent Publication No. 2009-238005    Patent Document 3: Japanese Laid-open Patent Publication No. 2002-10030    Patent Document 4: Japanese Laid-open Patent Publication No. 2003-187230